As is commonly known, a glass capillary tube for holding an optical fiber (hereinafter, glass capillary tube), in which an insertion hole is formed into which the optical fiber is inserted and held, is used for holding the optical fiber in alignment with an optical axis of an optical component such as optical waveguide-type device. The glass capillary tube is fixed to an end surface of the optical component in a straight line in such a way that a central axis of the insertion hole and the optical axis of the optical component are precisely positioned. In this case, both the optical component and the glass capillary tube are usually provided on the same flat surface of a substrate (or casing or holder).
As specific examples, Patent Document 1 below discloses a glass capillary tube of which an exterior surface is substantially rectangular in shape (composed of four flat portions) and in a center of which an insertion hole, into which a single-core optical fiber is inserted and held, is formed, and an optical component is connected to the glass capillary tube in a straight line. According to Patent Document 1, positioning of an optical axis of the optical fiber inserted into and held by the insertion hole, and an optical axis of the optical component, are determined by utilizing the flat portions on the exterior surface of the glass capillary tube.
Patent Document 2 below discloses a glass capillary tube of which an exterior surface is composed of a single flat portion and a single partial cylindrical portion, and in which an insertion hole, for inserting and holding an optical fiber corresponding to a central axis of the partial cylindrical portion, is formed, and a rectangular optical waveguide device is connected to the glass capillary tube in a straight line. According to Patent Document 2, in a state where an auxiliary member is fixed to an upper surface of a connecting end of the optical waveguide device, the flat portion of the glass capillary tube and a bottom surface of the optical waveguide device are provided on a base plane such that both are flushed with each other.
Patent Document 3 below discloses an optical waveguide device, of which a cross-section is approximately circular in shape, and a ferrule, of which a cross-section is approximately circular in shape for holding an optical fiber, provided such that respective end surfaces of the optical waveguide device and the ferrule are connected and held in an inner opening of a single sleeve, and an insertion hole in the ferrule into which the optical fiber is inserted and held is formed at a position deviated (de-centered) from a center of the ferrule.
[Patent Document 1] Japanese Unexamined Publication No. 2001-318270
[Patent Document 2] Japanese Unexamined Publication No. 2003-287651
[Patent Document 3] Japanese Unexamined Publication No. H2-236508